Abstract

A previously derived expression [Phys. Rev. A 40, 3898 (1989)] for the energy of arbitrary perturbations about arbitrary Vlasov–Maxwell equilibria is transformed into a very compact form. The new form is also obtained by a canonical transformation method for solving Vlasov’s equation, which is based on Lie group theory. This method is simpler than the one used before and provides better physical insight. Finally, a procedure is presented for determining the existence of negative‐energy modes. In this context the question of why there is an accessibility constraint for the particles, but not for the fields, is discussed.